bpo-45706: Add imaplib.IMAP4.login_plain by przemub · Pull Request #29398 · python/cpython · GitHub

Adds authentication using PLAIN SASL mechanism.

This is a plaintext authentication mechanism that can be used
instead of IMAP4.login() when UTF-8 support is required.

Issue: Add IMAP4.login_plain to imaplib #89869

Adds authentication using PLAIN SASL mechanism. This is a plain-text authentication mechanism which can be used instead of :meth:`IMAP4.login()` when UTF-8 support is required.

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This PR is stale because it has been open for 30 days with no activity.

Both tests passed.
Looks ok to me.

The module partially supports RFC 3501, which says that AUTH=PLAIN is mandatory. I understand that means advertising it in CAPABILITY is optional, so it might work regardless.

This sets the authorization identity (authzid) to the user name. Wouldn’t it be better to allow omitting authzid by default, let the server derive it? https://datatracker.ietf.org/doc/html/rfc4616#section-2

f'\x00{user}\x00{password}'.encode('utf-8')

Not sure that referring to RFC 6855 is that relevant. All it does is recommend against UTF-8 support with LOGIN, and say that AUTHENTICATE supports UTF-8.

This PR is stale because it has been open for 30 days with no activity.

…in_plain # Conflicts: # Lib/test/test_imaplib.py

The 'MD5 support is not available' note belongs to login_cram_md5, but merging placed it after login_plain, which was inserted between them. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Use an empty SASL authorization identity (RFC 4616): the previous code sent the user name as authzid, requesting proxy authorization, which many servers reject. * Note that PLAIN is only base64-encoded and requires a TLS connection. * Cite RFC 4616 for the mechanism; RFC 6855 only for UTF-8 support. * Fix the versionadded marker and the documented parameter name. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Documentation build overview

📚 cpython-previews | 🛠️ Build #33449956 | 📁 Comparing c0c2c29 against main (d733b10)

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3 files changed
± library/imaplib.html
± whatsnew/3.16.html
± whatsnew/changelog.html

RFC 3501 makes the PLAIN mechanism mandatory, so a server may support it without advertising AUTH=PLAIN in its CAPABILITY response. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

I synchronized the PR branch with main (it was 5 years!), addressed review comments by @vadmium, and made additional changes:

bytes is accepted as user and password, like in other login/authorization methods.
NUL is rejected in user and password. It conflicts with the delimiter.
Polished docs.

With all this it LGTM.

Thanks @serhiy-storchaka, @vadmium, @MaxwellDupre for fixes, reviews and support!

You are welcome!

bpo-45706: Add imaplib.IMAP4.login_plain

01330bd

Adds authentication using PLAIN SASL mechanism. This is a plain-text authentication mechanism which can be used instead of :meth:`IMAP4.login()` when UTF-8 support is required.

przemub requested a review from a team as a code owner November 4, 2021 00:44

the-knights-who-say-ni added the CLA not signed label Nov 4, 2021

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MaxwellDupre approved these changes Mar 3, 2022

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github-actions Bot added the stale Stale PR or inactive for long period of time. label May 11, 2026

serhiy-storchaka and others added 3 commits July 5, 2026 20:32

Merge remote-tracking branch 'upstream/main' into feature/imaplib/log…

c29bf20

…in_plain # Conflicts: # Lib/test/test_imaplib.py

Fix misplaced versionchanged note after the merge

7de847c

The 'MD5 support is not available' note belongs to login_cram_md5, but merging placed it after login_plain, which was inserted between them. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Soften the AUTH=PLAIN capability note and add a What's New entry

c0c2c29

RFC 3501 makes the PLAIN mechanism mandatory, so a server may support it without advertising AUTH=PLAIN in its CAPABILITY response. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

serhiy-storchaka requested a review from AA-Turner as a code owner July 5, 2026 20:05

serhiy-storchaka approved these changes Jul 5, 2026

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bedevere-app Bot added awaiting merge and removed awaiting core review labels Jul 5, 2026

serhiy-storchaka enabled auto-merge (squash) July 5, 2026 20:17

serhiy-storchaka merged commit 93b1a88 into python:main Jul 5, 2026
157 of 163 checks passed

bedevere-app Bot removed the awaiting merge label Jul 5, 2026

przemub mannequin mentioned this pull request Apr 10, 2022

Add IMAP4.login_plain to imaplib #89869

Closed

serhiy-storchaka mentioned this pull request Jul 5, 2026

can't use UTF8 passwords in imaplib login #93548

Closed

+                      """
+                      return self.authenticate(
+                          "PLAIN",
+                          lambda _: "{0}\x00{0}\x00{1}".format(user, password).encode()

bpo-45706: Add imaplib.IMAP4.login_plain by przemub · Pull Request #29398 · python/cpython · GitHub

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bpo-45706: Add imaplib.IMAP4.login_plain - #29398

bpo-45706: Add imaplib.IMAP4.login_plain#29398
serhiy-storchaka merged 5 commits into
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przemub:feature/imaplib/login_plain

przemub commented Nov 4, 2021 •
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+                  See :RFC:`6855`, page 5.
+                  It will only work if the server ``CAPABILITY`` response includes
+                  the phrase ``AUTH=PLAIN``.

+                  This is a plain-text authentication mechanism that can be used
+                  instead of :meth:`IMAP4.login()` when UTF-8 support is required.
+                  See :RFC:`6855`, page 5.

bpo-45706: Add imaplib.IMAP4.login_plain by przemub · Pull Request #29398 · python/cpython · GitHub

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bpo-45706: Add imaplib.IMAP4.login_plain - #29398

bpo-45706: Add imaplib.IMAP4.login_plain#29398serhiy-storchaka merged 5 commits intopython:mainpython/cpython:mainfrom przemub:feature/imaplib/login_plainprzemub/cpython:feature/imaplib/login_plainCopy head branch name to clipboard

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bpo-45706: Add imaplib.IMAP4.login_plain#29398
serhiy-storchaka merged 5 commits into
python:mainfrom
przemub:feature/imaplib/login_plain

przemub commented Nov 4, 2021 •
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